When crude oil is initially recovered from an oil-bearing earth formation, the oil is forced from the formation into a producing well under the influence of gas pressure and other pressures present in the formation. The stored energy in the reservoir dissipates as oil production progresses and eventually becomes insufficient to force the oil to the producing well. It is well known in the petroleum industry that a relatively small fraction of the oil in subterranean oil reservoirs is recovered during this primary stage of production. Some reservoirs, such as those containing highly viscous crude, retain 90 percent or more of the oil originally in place after primary production is completed.
A variety of conditions in the oil-bearing formation can impede the flow of oil through interstitial spaces in the oil-bearing formation, limiting the recovery of oil. In many cases, formations become damaged during the process of drilling wells into the formation. Mud, chemical additives and other components used in drilling fluids can accumulate around the well, forming a cake that blocks the flow of oil into the well bore. Drilling fluids can also migrate and accumulate in fissures in the formation, blocking the flow of oil through the formation. Parrafins and waxes may precipitate at the interface between the well bore and the formation, further impeding the flow of oil into the well bore. Sediments and native materials in the formation can also migrate and block interstitial spaces.
Numerous methods have been used to alleviate the problems associated with plugging in oil bearing formations. Plugging is often addressed by backflushing the well to remove mud from around the well. Backflushing the well can consume significant time and energy, and has limited effectiveness in unplugging areas that are located deep within a formation and away from the well. Acidizing the well and flushing the well with solvents are also used to alleviate plugging, but these methods can create hazardous waste that is expensive and difficult to dispose of. As a result, known methods for unplugging oil bearing formations leave much to be desired.
In many cases, crude oil is extracted with high concentrations of sulfur, polycyclic aromatic compounds (PAHs) and other compounds that reduce the quality and value of the oil. The presence of undesirable compounds in the oil requires subsequent processing of the oil, increasing the time and cost of production. Therefore, there is a great need to develop oil production methods that allow oil to be treated while it is being extracted.